Experimental Studies of Nonisothermal Binary Fluids With Phase Change in Confined Geometries

2012 ◽  
Author(s):  
Yaofa Li ◽  
Benjamin M. Chan ◽  
Minami Yoda
Keyword(s):  
Surface Tension ◽  
Mass Transport ◽  
Phase Change ◽  
Experimental Studies ◽  
Liquid Density ◽  
Binary Fluids ◽  
Vapor Interface ◽  
Evaporation And Condensation ◽  
Alcohol Water ◽  
Liquid Vapor

Evaporative cooling, which exploits the large latent heats associated with phase change, is of interest in a variety of thermal management technologies. Yet our fundamental understanding of thermal and mass transport remains limited. Evaporation and condensation can change the local temperature, and hence surface tension, along a liquid-vapor interface. The resulting thermocapillary stresses are dominant at small length scales in many cases. For the vast majority of single-component coolants, surface tension decreases as temperature increases, resulting in thermocapillary stresses that drive the liquid away from hot regions, leading to dryout, for example. The direction of flow driven by thermocapillary stresses is therefore consistent with that driven by buoyancy effects due to changes in the liquid density with temperature. However, a number of binary “self-rewetting fluids,” consisting of water-alcohol mixtures, have surface tensions that increase with temperature, leading to thermocapillary stresses that drive liquid towards hot regions, improving cooling performance. Although not all binary coolants are self-rewetting, all such coolants are subject to solutocapillary stresses, where differential evaporation of the two fluid components leads to changes in local species concentration at the liquid-vapor interface, and hence in surface tension. Given the lack of general models of thermal and mass transport in nonisothermal two-phase flows, experimental studies of convection in simple fluids and binary alcohol-water mixtures due to evaporation and condensation driven by a horizontal temperature gradient were performed. In these initial studies, both the simple and binary fluids have thermocapillary stresses that drive liquid away from hot regions. However, the binary fluid also has solutocapillary stresses that drive liquid towards hot regions. Particle-image velocimetry (PIV) is used to nonintrusively measure the velocity and temperature fields in a layer of liquid a few mm in depth in a 1 cm × 1 cm × 4.85 cm sealed and evacuated cuvette heated on one end and cooled on the other end.

Convection, Evaporation, and Condensation of Simple and Binary Fluids in Confined Geometries

2012 ◽  
Author(s):  
Tongran Qin ◽  
Roman O. Grigoriev
Keyword(s):  
Free Surface ◽  
Phase Change ◽  
Concentration Field ◽  
Major Effect ◽  
Binary Fluids ◽  
Homogeneous Fluid ◽  
Evaporation And Condensation ◽  
Numerical Studies ◽  
Alcohol Water ◽  
Convection Problem

Rayleigh-Bénard and Marangoni convection in a layer of a homogeneous fluid with a free surface in the absence of phase change is a classic (and extensively studied) problem of fluid mechanics. Phase change has a major effect on the convection problem. Most notably, significant latent heat generated at the free surface as a result of phase change can dramatically alter the interfacial temperature, and hence, the thermocapillary stresses. Furthermore, differential evaporation in binary fluids can lead to considerable variation in the concentration field, producing solutocapillarity stresses, which can compete with thermocapillarity and buoyancy. This talk describes numerical studies of convection in alcohol and alcohol-water mixtures due to a horizontal temperature gradient in the presence of phase change. We illustrate how the composition of the liquid and the presence of non-condensable gases (e.g., air) can be used to alter the balance of the dominant forces. In particular, by adding or removing air from the test cell, the direction of the flow can be reversed by emphasizing either the thermocapillary or the solutocapillary stresses.

On the Dependence of Surface Tension of Liquids on the Curvature of the Liquid−Vapor Interface

2001 ◽  
Vol 105 (5) ◽  
pp. 1050-1055 ◽  
Author(s):  
Vladimir B. Fenelonov ◽  
Gennady G. Kodenyov ◽  
Vitaly G. Kostrovsky
Keyword(s):  
Surface Tension ◽  
Vapor Interface ◽  
Liquid Vapor

scholarly journals Moses Effect (Deformation of Diamagnetic Liquid/Vapor Interface by Magnetic Field): Physics and Applications

2019 ◽  
Author(s):  
Edward Bormashenko
Keyword(s):  
Magnetic Field ◽  
Surface Tension ◽  
Experimental Techniques ◽  
Magnetic Memory ◽  
Self Healing ◽  
Near Surface ◽  
Vapor Interface ◽  
Macroscopic Properties ◽  
Liquid Vapor

Deformation of the surface of diamagnetic liquid by magnetic field is called the “Moses Effect”. Physics and applications of the direct and inverse Moses effects are reviewed. Experimental techniques enabling visualization of the effects are surveyed. Impact of magnetic field on micro- and macroscopic properties of liquids is addressed. Influence of the surface tension on the shape of the near-surface dip formed in a diamagnetic liquid by magnetic field is reported. Floating of diamagnetic bodies driven by the Moses effect is treated. The effect of the “magnetic memory of water” in its relation to the Moses Effect is discussed. The dynamics of self-healing of near-surface dips due to the Moses Effect is considered.

The Role of Surfactant Adsorption Rate in Heat and Mass Transfer Enhancement in Absorption Heat Pumps

2000 ◽  
Author(s):  
Michael S. Koenig ◽  
Gershon Grossman ◽  
Khaled Gommed
Keyword(s):  
Mass Transfer ◽  
Surface Tension ◽  
Heat And Mass Transfer ◽  
Heat Pumps ◽  
Surfactant Adsorption ◽  
Relaxation Rates ◽  
Dynamic Surface ◽  
Vapor Interface ◽  
Enhanced Absorption ◽  
Liquid Vapor

Abstract The importance of heat and mass transfer additives in absorption chillers and heat pumps has been recognized for over three decades. However, a universally accepted model for the mechanisms responsible for enhanced absorption rates has yet to be proposed. The Marangoni effect — an instability arising from gradients in surface tension at the liquid-vapor interface — is generally accepted as the cause of the convective flows that enhance transfer rates. Certain surfactant additives can significantly improve absorption rates and thus reduce the overall transfer area required by a given machine. Any means available that can increase the efficiency and acceptability of absorption machines is to be welcomed, as this technology provides an alternative to vapor compression systems which is both environmentally friendly and more versatile with regards to energy sources. This study investigates the rate at which a surfactant additive adsorbs at a liquid-vapor interface. The residence time of the falling liquid solution in an absorber is quite short. An effective additive must not only reduce the surface tension of the solution; it must do so quickly enough to cause the Marangoni instability within the short absorption process time. The entrance region of an absorber features a freshly exposed interface at which no surfactant has adsorbed. A numerical model is used to analyze surfactant relaxation rates in a static film of additive-laced solution. Kinetic parameters for the combination of the working pair LiBr-H2O and the additive 2-ethyl-1-hexanol are derived from data in the literature for static and dynamic surface tension measurements. Bulk, interfacial and boundary parameters influencing relaxation rates are discussed for surfactant adsorption occurring in the absence of absorption, as well as for concurrent adsorption and stable vapor absorption. Initial solution conditions and absorption driving force are shown to impact the potential for instability in the effect they have on the rate of interfacial additive adsorption.

Force Analysis of Bubble Dynamics in Flow Boiling Silicon Nanowire Microchannels

2016 ◽  
Author(s):  
Tamanna Alam ◽  
Wenming Li ◽  
Fanghao Yang ◽  
Ahmed Shehab Khan ◽  
Yan Tong ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Silicon Nanowire ◽  
Bubble Nucleation ◽  
Force Analysis ◽  
Vapor Interface ◽  
Liquid Vapor

In microchannel flow boiling, bubble nucleation, growth and flow regime development are highly influenced by channel cross-section and physical phenomena underlying this mechanism are far from being well-established. Relative effects of different forces acting on wall-liquid and liquid-vapor interface of a confined bubble play an important role in heat transfer performances. Therefore, fundamental investigations are necessary to develop enhanced microchannel heat transfer surfaces. Force analysis of vapor bubble dynamics in flow boiling Silicon Nanowire (SiNW) microchannels has been performed based on theoretical, experimental and visualization studies. The relative effects of different forces on flow regime, instability and heat transfer performances of flow boiling in Silicon Nanowire microchannels have been identified. Inertia, surface tension, shear, buoyancy, and evaporation momentum forces have significant importance at liquid-vapor interface as discussed earlier by several authors. However, no comparative study has been done for different surface properties till date. Detailed analyses of these forces including contact angle and bubble flow boiling characteristics have been conducted in this study. A comparative study between Silicon Nanowire and Plainwall microchannels has been performed based on force analysis in the flow boiling microchannels. In addition, force analysis during instantaneous bubble growth stage has been performed. Compared to Plainwall microchannels, enhanced surface rewetting and critical heat flux (CHF) are owing to higher surface tension force at liquid-vapor interface and Capillary dominance resulting from Silicon Nanowires. Whereas, low Weber number in Silicon Nanowire helps maintaining uniform and stable thin film and improves heat transfer performances. Moreover, force analysis during instantaneous bubble growth shows the dominance of surface tension at bubble nucleation and slug/transitional flow which resulted higher heat transfer contact area, lower thermal resistance and higher thin film evaporation. Whereas, inertia force is dominant at annular flow and it helps in bubble removal process and rewetting.

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